Conventional power supply apparatus for plasma arc utilizing equipment, e.g. a plasma arc cutter or a plasma arc welder, typically has the following arrangement. A rectifier rectifies an AC voltage to generate a rectified voltage, which is converted into a high frequency voltage by a half-bridge inverter including capacitors and switching elements. The high frequency voltage is, then, voltage-transformed by a transformer. The transformed high frequency voltage is rectified by a second rectifier and, then, applied to a torch of the equipment and a workpiece to be wrought, so that arc is generated therebetween. A current detector detects current flowing between the torch and the workpiece during arcing, and provides a signal representative of the current. The current representative signal is applied to a control circuit for controlling the inverter. The control circuit controls switching elements of the inverter such that the current representative signal becomes equal to a signal representative of a preset current.
Such power supply apparatus has a low power factor because it employs a half-bridge inverter including capacitors. The power supply apparatus provides a high output voltage because it is controlled to provide a constant current, and, therefore, it provides a small output current relative to an input current applied thereto.
Accordingly, an object of the present invention is to provide power supply apparatus which can provide a large output current.